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4 of 6 Welding in the World
Volume 51, Issue SPEC. ISS., 15 July 2007, Pages 667-676
Formability of steel and aluminium tailor
welded blanks
Rodrigues, D.M. , Chaparro, B.M. , Leitão, C. , Baptista, A.J.,
Loureiro, A. , Vilaça, P.
Abstract
In the industrial production of metallic components by plastic
deformation processes, the introduction of the Tailor-Welded Blank
(TWB) technological concept enabled, simultaneously, the production
of stronger and light panels and the reduction of material waste,
which is an important step in nowadays environmental concerns.
However, it is well know that existing welding technologies can
induce significant differences in mechanical properties between the
welds and the base materials. An important question in current
investigation on TWBs formability is whether the weld bead, that
can vary from very wide to very narrow, according to the weld
process in use, has a significant influence on the overall plastic
behaviour of the welded blanks. In this investigation the
formability behaviour of Laser steel welded blanks, with narrow
weld beads, and Friction Stir Welded (FSW) aluminium blanks, with
wide weld beads, will be compared. The base materials are two Steel
Alloys (DC06 and DP600) and two Aluminium Alloys (AA 5182-H111 and
AA 6016-T4) very popular in automotive industry. The TWBs were made
from 1 mm thick plates by considering similar (DP600/DP600,
DC06/DC06, AA 5182-H111/ AA 5182-H111 and AA 6016-T4/ AA 6016-T4)
and
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dissimilar (DP600/DC06 and AA 6016-T4/ AA 5182-H111)
combinations of both types of base materials. The formability
behaviour of the TWBs was analysed by stamping Axissimetrical
Cylindrical Cups in a Deep-Drawing laboratorial testing device
specially developed to work in a classical tensile test machine.
The main reported results were the punch force-displacement curves
and geometrical data from the Axissimetrical Cylindrical Cups.
Results from the formability tests in all type of welds are
presented and compared in the paper.
Author Keywords
Formability; Laser welding; Taylor welded blanks; Friction stir
welding
Matched Terms:
Index Keywords: Laser beam welding See the Extended format page
for all index keywords in this document.
References (6) view in table layout
Select: Page
1. Jambor, Arno, Beyer, Matthias New cars - new materials (1997)
Materials and Design, 18 (4-6), pp. 203-209. Cited 21 times.
2. Saunders, F.I., Wagoner, R.H. Forming of tailor-welded blanks
(1996) Metallurgical and Materials Transactions A: Physical
Metallurgy and Materials Science, 27 (9), pp. 2605-2616. Cited 32
times.
3. Ghoo, B.Y, Keum, Y.T, Kim, Y.S Evaluation of the mechanical
properties of welded
metal in tailored steel sheet welded by CO laser (2001) Journal
of Materials Processing Technology, 113 (1-3), pp. 692-698. Cited
11 times. doi: 10.1016/S0924-0136(01)00674-4
4. Kampuš, Z., Balič, J. Deep drawing of tailored blanks without
a
blankholder (2003) Journal of Materials Processing Technology,
133 (1-2), pp. 128-133. Cited 5 times. doi:
10.1016/S0924-0136(02)00215-7
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Policy Copyright © 2008 Elsevier B.V. All rights reserved. Scopus®
is a registered trademark of Elsevier B.V.
5. Menezes, L.F., Teodosiu, C. Three-dimensional numerical
simulation of the
deep-drawing process using solid finite elements (2000) Journal
of Materials Processing Technology, 97 (1-3), pp. 100-106. Cited 42
times. doi: 10.1016/S0924-0136(99)00345-3
6. Akselsen, O.M., Rorvik, G., Onsoien, M.I., Grong, O.
Assessment and predictions of HAZ tensile
properties of high-strength steels (1989) Welding Journal
(Miami, Fla), 68 (9), pp. 356s-362s. Cited 7 times.
© Copyright 2008 Elsevier B.V., All rights reserved.
Welding in the World
Volume 51, Issue SPEC. ISS., 15 July 2007, Pages 667-676 4 of
6
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FORMABILITY OF STEEL AND ALUMINIUM TAILOR WELDED BLANKS
OM Rodrigues ', BM Chaparro'?', C Leitao", AJ Baptista ', A
Loureiro' , P Vilaya 3
CEMUC, Department of Mechanical Engineering, University of
Coimbra, Portugal ESTA, Polytechnic Institute of Tomar, Abrantes,
Portugal
OEM, 1ST, Technical University of Lisbon, Portugal
Keywords: Taylor welded blanks; Friction stir welding; Laser
welding, Formability
Abstract: In the industrial production of metallic components by
plastic deformation processes, the introduction of the
Tailor-Welded Blank (TWB) technological concept enabled,
simultaneously, the production of stronger and light panels and the
reduction of material waste, which is an important step in nowadays
environmental concerns. However, it is well know that existing
welding technologies can induce significant differences in
mechanical properties between the welds and the base materials. An
important question in current investigation on TWBs form abil ity
is whether the weld bead , that can vary from very wide to very
narrow, according to the weld process in use, has a significant
influence on the overall plastic behaviour of the welded
blanks.
In this investigation the formability behaviour of Laser steel
welded blanks, with narrow weld beads, and Friction Stir Welded
(FSW) aluminium blanks, with wide weld beads, will be compared. The
base materials are two Steel Alloys (DC06 and DP600) and two
Aluminium Alloys (AA 5l82-Hlll and AA 60l6-T4) very popular in
automotive industry. The TWBs were made from 1 mm thick plates by
considering similar (DP600/DP600, DC06/DC06 , AA 5182-Hll1 1 AA
5l82-Hlll and AA 60 I6-T41 AA 6016-T4) and dissimilar (DP600/DC06
and AA 6016-T41 AA 5182-Hlll) combinations of both types of base
materials.
The formability behaviour of the TWBs was analysed by stamping
Axissimetrical Cylindrical Cups in a Deep-Drawing laboratorial
testing device specially developed to work in a classical tensile
test machine. The main reported results were the punch
force-displacement curves and geometrical data from the
Axissimetrical Cylindrical Cups . Results from the formability
tests in all type of welds are presented and compared in the
paper.
667
-
1. INTRODUCTION
Due to the worldwide extreme competitiveness and severe
governmental regulations, metal forming companies suffer today
increased pressures to achieve, simultaneously, high quality
products, minimal costs and minimum material waste and pollutant
emissions. In the particular case of the automotive industry
important efforts have been made to develop new technological
solutions that enabled the employment of lighter materials, such as
aluminium alloys, polymers or high strength steels, and also to
produce components adopting new technological processes, such as
hydroforming, powder injection moulding or improved welding
technologies, which allow the use of optimized blanks, such as the
tailor-welded blanks (TWBs).
The TWBs technological concept consists in producing panels
composed by several sheet metal blanks that may be of different
material grades, strengths, gauge thickness or coatings, welded
together prior to the forming process. The key advantage of using
TWBs is the attained weight reduction, due to the fact that only
the strictly necessary material (and implicitly only the strictly
necessary mechanical resistance) is applied to each panel area, for
a predefined overall resistance of the global formed part [I ].
Despite of the technological process of TWBs has over 25 years
of automotive applications, several difficulties continued
constraining its general use in industry. Some of those
difficulties have been:
• The decreased formability of the welded panel when compared
with a non-welded one; • The difficulty of welding some materials
without defects or strength reduction on the
weld line (aluminium alloys and high strength steels specially);
• The required high precision of the edges to align joints for
laser welding (higher costs).
It is also well established that the combination of blanks with
dissimilar characteristics leads to different thermal behaviour
during the welding operation which, sometimes, give rise to welds
with substantially different mechanical properties face the base
materials. Thus, an important question is whether the weld bead has
a significant influence on the overall forming behaviour of the
welded blanks [2-4].
In this study, the formability behaviour of aluminium and steel
TWBs and its relation with the weld bead width and mechanical
properties was addressed by performing deep-drawing tests . Steel
TWBs with narrow welds were produced by using the Diode Laser
technology . Aluminium Friction Stir Welded TWBs were fabricated in
order to obtain blanks with wide weld beads. The base materials
were two Steel Alloys (DC06 and DP600) and two Aluminium Alloys (AA
5182-HIII and AA 6016-T4) very popular in automotive industry. The
TWBs were made from I mm thick plates by considering similar
(DP600/DP600, DC06/DC06, AA 5182-HIIlIAA 5182-HIII and AA
6016-T4/AA 6016-T4) and dissimilar (DP600/DC06 and AA 6016-T4/AA
5182-H I I I) combinations of both types of base materials.
2. WELDING PROCEDURE
Steel Tailor Welded Blanks: The welds were produced in steel
sheets using a Rofin high power diode laser of 3 kW adapted to a
Kuka robot. No filler wire was used in the welds. The weld
direction was settled parallel to the rolling direction in the
similar TWBs (DP600/DP600, DC06/DC06) and perpendicular to the
rolling direction in the dissimilar TWBs (DP600/DC06) . The welding
parameters were: working distance 44 mm; rectangular focus size
(0.8x 1.2 mm) ; welding speed 18 mrn/s . Inert shielding gas was
used (8 It/min) and the sheets were clamped alongside at a short
distance from the weld.
Aluminium Tailor Welded Blanks: Friction stir welded tailored
blanks were made from aluminium plates by using a 10 mm shoulder
diameter tool with a threaded pin of 3 mm in diameter and I mm in
length. The welding conditions were: 1800 rpm rotation speed (m),
160 mrnlmin travel speeds (v), 0.9 ~ I mm tool penetration and 2.so
tool tilt angle. Also in this case the welds were performed
considering similar (AA 5182-H 111/AA 5182-H III and AA 6016T4/AA
6016-T4) and dissimilar (AA 5182-HIIl/ AA 6016-T4) combinations of
the base materials. The weld direction was set parallel to the
rolling direction of the sheets in all types of
. TWBs. The sheets were clamped alongside at a short distance
from the weld line.
668
-
3. TESTING PROCEDURE
Befor e the formab ili ty test s, the heterogen eity in mech an
ical prop erties across the d iffere nt wel d zo nes was assessed
by perform ing hardn ess tests . Hardness mea surem ents were pe
rformed tran sv ersely to the we ld directi on , for a ll the welds
, usin g load va lues opt im ized accordi ng to the base materi al
in s tudy: 200 g for the two Stee l base materials, SOg for the AA
S182-Hll I a lum ini um a lloy and 100 g for the AA 60 16-T4 a
lumini um all oy. A ll the res ults were verified by performing,
for each type of sa mp le, hardn ess measurem ents in severa l pos
itions along the welding d irecti on s.
The formability beh aviour of the tail ored bl anks and homogen
eous base material s was studied by sta mping Ax isy me trica l
Cylindrical Cups in a lab oratorial deep drawing devi ce spec iall
y developed to work in a c lass ica l ten sil e test mach ine . To
perform the for ma bi lity tests c ircula r specimens with 200 mm
diam ete r we re extr acted fro m the pa rent materi al shee ts and
from the TWBs (Fig ure 1).
The stam ping tool, sho wn in F igure 2, ena b le to app ly and
maintain the force in the blank-holder, by usin g 10 calibrat ed
springs . O ne of these spr ings is equ ipped with a IOkN fo rce
sensor in orde r to verify if the blank hold er fo rce rem ain s
sta ble during the test. Th e s tampi ng operati on wa s always
perfo rm ed on lubri cated blanks . It was app lied 1.4 g/m 2 of
QUAKER N61 30 o il per blank face us ing a pre- impregnated pap er
weighted before and afte r the applicat ion . The admiss ible error
on lubricant weighing was less than S %. The base ma te ria ls and
the tailored blanks were tested usin g the followi ng testing cond
itions : 100 rum/min pun ch speed in all tests and 16 kN clamp ing
force for the DC06 spec imens , 28 kN for the DP 600 and DC-DP600
blan ks, and finall y, 8kN fo r a ll typ es of A lumi nium A lloy
spec imens. The clampi ng forc e was previou sly optim ized by
using base materi al sam ples o f both types of Steels and Alum in
ium a lloys .
o CD CD a) Base Material Sample c) Similar weld TWB e)
Dissimilar weld TWB
Figure I - Schem at ic re prese nta tion o f the spe cimens used
in the formabilit y test.
' 00
r .. . ·.. ,·1..I . ,
,I I', I
'. : _ . •_. : : ,~ _ .. c_ t. , ._. - " ' -" " ~ .'-=:J
, J
_ . ;J
' 1 10
-_ - -l
Figure 2 - Stamping tool.
4. RESULTS AND DIS CUSSION
4.l Hardness tests
The hardness evo lution across the we lds is shown in Figures 3
and 4 for the Ste el and Aluminium ta ilored blan ks, respectively.
Th e average hardness determined for each
669
-
base material were: 122 HYO.2 for the DC06 steel, 223 HYO.2 for
the DP600 steel , 71 HYO.05 for the AA 5182-Hl11 aluminium and 67
HYO.1 for the AA 6016-T4 aluminium. The weld limits , corresponding
to the melted material (MM) and heat affected zone (HAZ), for the
steel laser welds, and to the under tool shoulder area, for the
friction stir solid state aluminium welds , are delimited in each
graph by grey bars.
The hardness results for the similar DC06 welded blanks, see
figure 3.a, show an increase in hardness in the melted material
area (150 HYO.2) relative to the base material (122 HYO.2). The
hardness increase is limited to the approximately 3 mm width melt
material line. The hardness results for the DP600 welded blanks
show a quite different evolution, as it is illustrated in figure
3.b. In fact, strong heterogeneity in properties was registered
across de weld, being possible to observe a significant increase in
hardness in the melt material area (280 HYO.2) and some softening
in the heat-affected zone (208 HYO.2) relative to the base material
(223 HYO.2). The mechanical heterogeneity area has approximately 7
mm width , with the hardness values falling progressively from the
base material to the HAZ and rising abruptly in the melted
material. Finally, the hardness profile for the DC06IDP600
dissimilar TWB is displayed in figure 3.c. The hardness evolution
for this weld matches closely with those observed for the similar
welds, being possible to observe a jump in hardness inside the
molten metal area (300 HYO.2). After these observations an
important issue is whether such a sudden change in hardness,
concentrated in a narrow region, can have some influence in the
plastic deformation behaviour of the similar and dissimilar
TWBs.
Analysing now the results plotted in Figure 4.a and 4.b, for the
similar aluminium TWBs, it is possible to conclude that there are
very small differences in hardness between the welds and the base
materials, for both similar welds, which indicate that the FSW
process induces very small changes in mechanical properties in the
weld area, for this type of materials and welding conditions. In
the same way, for the dissimilar weld (Fig. 4.c) it is possible to
observe a smooth hardening transition transversely to the weld line
that joints together de different base materials. In fact , the
hardness values in the weld fall between the average hardness
values characteristic of each base material. From the hardness
results it is possible to expect a relatively good homogeneity in
macroscopic mechanical properties for both similar and dissimilar
aluminium TWBs. However, it is important to enhance that the
welding process induces locally severe changes in material
microstructure and surface finishing (due to the marks left by the
rotating tool) and also to a small cross section decrease in the
weld, as it is possible to see in Figure 5. This material and
geometrical heterogeneities extends over a 10 mm width weld area
and can affect the plastic deformation behaviour of the blanks
during the forming process.
4.2 Formability tests
Figure 6 presents the punch force-displacement evolution for the
steel TWB samples and also the results obtained with homogeneous
base material specimens. It can be observed that the curves for the
similar welds (TWB_DP600 and TWB_DC06) and homogeneous base
material specimens (DP600 and DC06) are very close and the maximum
drawing force values are almost the same for both types of samples.
The pictures of the drawn cups obtained from the monolithic DC06
material and DC06/DC06 welded blank are shown in figures 7.a and
7.b, respectively. The central hole in each sample was machined
with the aim to assist the blank positioning in the deep-drawing
device. From the force-displacement graph and from the pictures it
is possible to conclude that despite the strong heterogeneity in
mechanical properties in the welds, revealed by the measured
hardness profiles, the similar TWBs can be formed with success
using the same stamping parameters of the base materials.
670
-
DC 06/ DC 06
190
N o > J:
'" '" Q)c:"E . 110 1 m J:
, 90 -t . .
70 I
·10 -8 -6 -4 -2 0 2 4 6 8
Distance from the weld center line [mm]
a)
DP 600 J DP 600
N o >J:
~ Q) c: .. "2... J:
r----,----,--~;--:'_r_--..,..........- 180.....
~.-"""-,.---,----,...,- --,.,.--- --,
-10 -8 -6 -4 -2 0 2 4 6 8 10
Distance from the weld center line [mm)
. I b)
--- .- --- --- - - --·--------------·-------- ·--- - - --- -
---1
N
g J:
'" &l c: "2 m J:
.----,---.- -. - ,--100-1r----;----,.----.--- -,----,
I -10 -8 -6 -4 -2 0 2 4 6 8 10 I l' Distance from the weld
center line [mm]
c)
Figure 3 - Hardness profile across the DC061 DC06 (a), DP6001
DP600 (b) and DC061 DP600 (c) welds.
671
-
• ••
AA5182-H111! AA5182-H111
~
1o cc o ... . .;" ...., , , ~ .. ..., .. .g .........,. .. . . -
. I en en OJ c "E ell I o
LO
- _..__ .. ~ . -15 -10 -5 o 5 10 15
Distance from weld center line (mm)
a)
AA 6016-T4! AA 6016-T4 o Ol
• • +.0 1 . •. .... .. . ._......... . ci ........, "'.''''. ' •
, • .. > ••I o en CD •en OJ
, c
I ~ - ----- - . Sif·
~ -15 -10 -5 o 5 10 15
Distance from weld center line (mm)
b)
AA5182-H111! AA6016-T4
U)
"- ....... . . - .g . ..., .,. ~.. -~
..~ . -........, ..I -. - ..~,. ~.en •en OJ •c • • "0
10 •I
-15 -10 -5 o 5 10 15
Distance from weld center line (mm)
c)
Figure 4 - Hardness profile acros s the AA 5182-H 11 1/ AA
5182-H 111 (a), AA 6016-T4/ AA 60 16-T4 (b) and AA 5182-Hll 1/ AA
6016-T4 (c) welds.
672
-
AA5l82-Hlll AA 5l82-Hlll
AA 60l6-T4 AA 6016-T4
Figure 5 - Appearance of the surface and cross section of the
similar aluminum welds.
In the case of the TWB composed by dissimilar materials
(TWB_DC_DP600), the initial punch force-displacement curve lays, as
expected, between the DC06 and DP600 curves. However, for this
sample, the full punch displacement was not attained due to the
rupture of the weld after 20 mm stroke, as it is possible to see in
the picture of figure 7.c . In order to understand the dissimilar
TWB behaviour during the stamping test a numerical simulation
reproducing the experimental test was performed by using an
implicit three dimensional finite element program (DD3IMP [5]). The
material parameters used in the numerical simulation are those
presented in Table 1 for both base materials and for the weld line
. The material constants for the weld material zone were estimated
from the hardness results by using the procedure described in
[6].
According to the numerical simulation results, the rupture of
the dissimilar TWB cup can be justified by different deformation
behaviour of the materials, and also, by the presence of the center
hole used to assist the positioning of the blank. In figure 8 is
shown a picture of the equivalent plastic strain distribution in
the sample in which it is possible to observe strong strain
concentration near the weld line next to the hole . Numerical
result shown that combining constraint induced by the hole with the
smaller strength resistance of the DC06 face the DP600 material,
significant thickness reduction takes place on DC06 weld side
leading to failure along the weld as observed in the experimental
test.
200
160 Z 2'S Q) 120t! 0 u, .J::: U c 80 ::J CL
40
Punch Displacement [mm]
-D-DC06 --¢-TWB_DC06 ----6-DP600 -o-TWB_DP600 --TWB_DC-DP600
Figure 6 - Punch force versus punch displacement curves for the
different sets of steel TWBs tested and for the DC 06 and DP 600
base materials.
673
-
~ ~ 0 Figure 7 - Deep-drawing cups of (a) DC06 base material,
(b) DC06 similar weld and
(c) DP600/DC06 dissimilar weld.
a - . I d' h I' I'T bl e 1 Matena parameters use In t e numenca
simu anon. DC06 DP600 DC/DP weld
Young modulus - E GPa) 210 Poisson coefficient - v 0.30
Yield stress - 0"0 (MPa) 123.6 359.38 810 .9 Hardening law K
(Mpa) 529.5 1098.34 1280.1
(J" = K(co + c)" Co n
0.00438
0.268
0.00145
0.171
0.0205
0.117
y
2
0.675 0.600 0.525
·0.450 . 0 .375
0.300 0 .225 0.150 0.075 o
X
Figure 8 - Equivalent plastic strain distribution in the
DC06/DP600 dissimilar TWB.
In Figure 9 are shown the punch force-displacement curves for
the similar aluminium welds and for the two aluminium base
materials. Analysing the graph it is possible to conclude that the
punch force evolution for both similar welded blanks is very close
to that of the correspondent base materials, until around 20 mm
punch displacement. After 20 mm punch displacement strong wrinkling
started in both TWBs, accompanied by a strong decrease in the punch
force relative to the base materials. In figure 10 is possible to
compare the cups obtained for the AA 5182-H 11 material: Base
material cup (Figure 1O.a) and the inner and outer surface (Figure
10. band c, respectively) of the similar TWB cup. As it is
exemplified in this figure , no necking was observed in the weld
zone for both tailored blanks, which confirms the good deformation
behaviour of these solid state welds. However, the occurrence of
wrinkling establishes the necessity of optimizing the stamping
parameters for the tailored blanks,
674
-
even when the hardness results suggest relative homogeneous
behaviour between the weld line and the base materials. Since it
was not possibl e to get the deep-drawing of the similar weld s, no
experiment was performed with de dissimilar weld specimens.
90
80
70
Z 60 ~ o 50u 0 u, s: 40 u C ::J
300
20
10
0 0 10 20 30 40 50 60 70
Punch Displacement [mm]
0 - AA 5182 -0- AA 6016
Figure 9 - Punch force versus punch displac ement curves for the
different sets of similar aluminium TWB s and for the AA 5182 HIll
and AA 60 16-T4 base materials.
a) b) c)
Figu re 10 - Deep-drawing cups of AA 5l82-H11 base materi al (a)
and outer (b) and inner (c) surfaces of the similar AA 5182-H l l
weld cup.
It is well known that the most frequent types of failure in the
deep-d rawing of metallic components are wrinkling, neckin g (and
subsequently tearin g), scratching and ora nge peel. All this
failur e mechani sms can be attr ibuted to an incorrect design of
the tools and blank shape or to an incorrect choice of material ,
lubr icat ion and process parameters. The process param eters in
this experimental study were previously opt imized by using
homogeneous base materials sampl es and several base material cups
were formed with success. However it was not possible to obtain
correctly formed parts from the TWB s, by using the same process
parameter conditi ons. A numerical study is currently bein g
performed in order to optimi ze the blank shape and blank-holder
farc e for the stamping of the TWB s.
675
-
5. CONCLUSIONS
Based on the results presented in this paper, it is possible to
conclude that the formability behaviour of the TWBs depends mainly
on the mismatch in mechanical properties bet ween the ba se
materials joined together, on the we ld width and on the macro and
microstructure of the tailored blanks. In current study it was
possible to perform with success several axissimetrical cups with
the DC06 and DP600 base materials and its similar welds. The same
process parameters were used for the stamping of the homogeneous
(base material) and welded specimens. The results obtained shows
that a strong mismatch in mechanical properties, if localized in a
narrow weld zone (as indicated by the hardness profiles registered
for these materials), doesn't have any influence on the formability
behaviour of the tailored blanks. However, if the two different
steels are joined together, the plastic behaviour of the dissimilar
TWB is substantially different from the similar ones. In fact,
rupture of the dissimilar welded blanks was observed under the same
deep-drawing conditions of the similar blanks. From the results of
the numerical simulation of the experimental test it is expected
that changing the blank shape, more precisely, removing the central
hole of the blank, it will be possible to shape with success the
dissimilar TWBs.
The results obtained from the formability tests of the AA 5182-H
III and AA 6016-T4 base materials and its similar welds shown a
different type of behaviour from that registered with the steel
samples. In fact , despite the relative homogeneity in mechanical
properties across the we lds revealed by the hardness measurements,
the similar TWBs suffer strong wrinkling under the same test
conditions of the base materials. This behaviour can be associated
with severe changes in material microstructure, surface finishing
and thickness of the weld relative to the base material , which
induces non-homogeneous behaviour of the blank. Optimization of the
process parameters for the stamping of the aluminium TWBs is
currently in progress .
ACKNOWLEDGMENTS
The authors are indebted to the Portuguese Foundation for the
Science and Technology (FCT) and FEDER for the financial support
through the POCI program and to Novelis Switzerland SA for
supplying the aluminium sheets.
REFERENCES
[I] A. Jambor, M. Beyer, New cars - new materials , Materials
& Design,Vol. 18, 4/6 (1997) 203-209.
[2] F.L Saunders, R.H. Wagoner, Forming of Tailor-Welded Blanks.
Metallurgical and Materials Transactions A, Vol. 27 A (1996) 2605
.
[3] B.Y Ghoo, YT. Keum, YS . Kim, Evaluation of the mechanical
properties of welded metal in tailored steel sheet welded by C02
laser, Journal of Materials Processing Technology, 113
(2001),692-698.
[4] Z. Kampus, 1. Balic, Deep drawing of tailored blanks without
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